This ongoing program of research on human visual information processing is currently concentrating on elucidating and describing visual selective attentional mechanisms. This empirical knowledge is a necessary first step in the development of a comprehensive model of attention. Specific issues addressed in the present proposal are: 1) the degree of processing of nonattended stimuli; 2) negative priming and the degree to which selection depends upon active suppression of irrelevant stimuli; 3) whether focal attention has a minimal channel size; 4) whether focal attention is best conceived as unitary and constant or as comprising different levels; and 5) the spread or distribution of attention in the visual field. Many of the methodologies employed in the research make use of procedures and paradigms that we have developed in our laboratory such as precueing, response competition and stimulus substitution. In certain multi-variate experiments electromyographic recordings and evoked brain potentials are used along with measures of response latency and accuracy. We will also employ measures based upon the microstructure of simple responses such as lever movements that the subjects use to signify their choices or decisions. Past work in our laboratory has shown the value of these micro responses in revealing processing differences that are not apparent when only RT or accuracy is looked at.